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Metal-insulator transitions (MITs) in doped uncompensated systems are investigated in the Mott–Hubbard and Anderson impurity models by considering the intercarrier correlation and screening effect of carriers in the same hydrogenic impurity center, the formation of the superlattices with different coordination numbers (z=6, 8 and 12) and by studying the effect of randomness in impurity distribution. We have obtained simple and quite general criteria for the Mott and Anderson transitions and used these criteria to describe quantitatively the correlation and disorder-induced MITs in doped semiconductors and high-T c cuprates. We examine the validity of the obtained criteria for the Mott and Anderson MITs in these doped systems. It is found that the newly derived criteria for the Mott MIT are well satisfied in doped semiconductors, but they cannot be used to describe the observed MITs in the hole-doped high-T c cuprates, whereas the newly derived criteria for the Anderson MIT are applicable equally to describe the MITs observed both in doped semiconductors (at weak and intermediate disorders) and in doped cuprates (at intermediate and strong disorders). The new criteria for the Anderson MIT are extended to the polaronic systems in p-type cuprates. Our results are in quantitative agreement with the existing well-established experimental data and shed more light on the different types of MITs that occur in doped uncompensated semiconductors and cuprates.

Here we consider an interacting electron-phonon system within the framework of extended Holstein-Hubbard model at strong enough electron-phonon interaction limit in which (bi)polarons are the essential quasiparticles of the system. It is assumed that the electron-phonon interaction is screened and its potential has Yukawa-type analytical form. An effect of screening of the electron-phonon interaction on the temperature of Bose-Einstein condensation of the intersite bipolarons is studied for the first time. It is revealed that the temperature of Bose-Einstein condensation of intersite bipolarons is higher in the system with the more screened electron-phonon interaction. PACS. 71.38.Mx -Bipolarons, 74.20.Mn -Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.), 03.75.Lm -Tunneling, Josephson effect, BoseEinstein condensates in periodic potentials, solitons, vortices, and topological excitations

Epitaxy layers of solid solution (ZnSe) 1-x-y (Si 2 ) x (GaP) y (0  х  0.03, 0  y  0.09) were grown up from the limited volume of tin solution-melting by method of liquid phase epitaxy. Profiles of distribution of components Ga, P, Zn, Se and Si in grown up epitaxy layers are defined. In spectrum of the photoluminescence of surface of the solid solution at 5 K 2 peaks of radiation are found out. They are probably caused by compounds Si 2 (1.67 eV) and GaP (2.21 eV). It has been shown that covalent coupling Si-Si and Ga-P cause impurity levels laying in the forbidden zone of the solid solution (ZnSe) 1-x-y (Si 2 ) x (GaP) y . Isotype heterojunction n-GaPn09) (without luminophor) gives red and yellow luminescence which is caused by electronic transitions from Si-Si and from Ga-P, taking place in tetrahedron lattice of the solid solution.